Oxygen-etched Fe-NC cathode oxygen reduction catalyst and its preparation method and application

Abstract

The present disclosure proposes a method for preparing an oxygen-etched Fe-N-C cathode oxygen reduction catalyst, comprising: performing a first pyrolysis on ZIF-8 in a protective atmosphere to obtain a nitrogen-carbon substrate, wherein the nitrogen-carbon substrate has a regular dodecahedral framework structure; dispersing the nitrogen-carbon substrate, superoxide and crown ether in a solvent to obtain a suspension, in which the superoxide releases superoxide ions, and the superoxide ions form carbon-oxygen double bond defects with carbon atoms in the nitrogen-carbon substrate, and the suspension is centrifuged to obtain a composite solid; after grinding and mixing the composite solid with an iron salt, performing a second pyrolysis in a protective atmosphere, and after acid washing and drying, obtaining an oxygen-etched Fe-N-C cathode oxygen reduction catalyst. The present disclosure also proposes a Fe-N-C cathode oxygen reduction catalyst obtained by the above-mentioned preparation method and its application.

Description

Technical Field

[0001] The present disclosure belongs to the technical field of catalysts and their preparation, and particularly relates to an oxygen-etched Fe-NC cathode oxygen reduction catalyst and a preparation method and application thereof. Background Art

[0002] Fuel cells are hailed as the most important new energy technology of the 21st century due to their high energy conversion efficiency, clean operation, and environmentally friendly properties. However, the oxygen reduction reaction (ORR) in fuel cells' cathodes is extremely slow, becoming a bottleneck in their operation. While the precious metal Pt can effectively catalyze the ORR, its high cost makes the development of non-Pt catalysts particularly important.

[0003] Fe-NC single-atom catalysts are often considered promising candidates to replace precious metal Pt-based catalysts and have garnered widespread attention. However, compared to Pt-based catalysts, Fe-NC single-atom catalysts have a lower active site density, making them difficult to adapt to the high power loads required by fuel cells. This is primarily due to the limited metal atom vacancies on the nitrogen-carbon substrate, which makes it difficult to accommodate a high density of Fe single atoms. Furthermore, the high specific surface energy of the metal makes Fe particles prone to agglomeration during high-temperature sintering in pyrolysis-type catalysts, further reducing the dispersion of Fe atoms.

[0004] In the relevant technologies, the main methods to increase the density of Fe single-atom sites are: using vapor deposition technology to allow FeCl3 vapor to directly participate in the transformation of Zn-N4 sites on the nitrogen-carbon substrate to Fe-N4, thereby obtaining an Fe-based single-atom catalyst with high active site density and gas-phase accessible sites; treating nitrogen-carbon by heating, pickling, reflux and adding dicyandiamide to remove Zn sites in the nitrogen-carbon substrate and increase the nitrogen content of the anchoring metal, and finally obtaining a high-performance Fe-based single-atom catalyst with a metal loading of 7 wt%; using an H2 pyrolysis environment to promote the deoxygenation and dechlorination of nitrogen-carbon and metal precursors, thereby realizing the formation of Fe single-atom sites at a lower temperature of 360 °C, avoiding the formation of metal particles at high temperatures.

[0005] Although the single-atom catalysts prepared above have high loadings, a simple process for achieving high single-atom density based on nitrogen-carbon substrate regulation is still lacking. Therefore, finding a Fe-NC single-atom catalyst with simple process and high active center density has far-reaching practical significance. Summary of the Invention

[0006] In view of this, in order to solve at least one technical problem in related technologies and other aspects, the present disclosure proposes a method for preparing an oxygen-etched Fe-NC cathode oxygen reduction catalyst, comprising:

[0007] In a protective atmosphere, ZIF-8 is subjected to a first pyrolysis to obtain a nitrogen-carbon substrate, wherein the nitrogen-carbon substrate has a regular dodecahedral framework structure;

[0008] The nitrogen-carbon substrate, superoxide and crown ether are dispersed in a solvent to obtain a suspension, in which the superoxide releases superoxide ions, which form carbon-oxygen double bond defects with carbon atoms in the nitrogen-carbon substrate, and the suspension is centrifuged to obtain a composite solid;

[0009] The composite solid is ground and mixed with iron salt, and then subjected to a second pyrolysis in a protective atmosphere. After acid washing and drying, an oxygen-etched Fe-NC cathode oxygen reduction catalyst is obtained.

[0010] According to an embodiment of the present disclosure, the preparation method of ZIF-8 includes:

[0011] Mixing a methanol solution of zinc nitrate hexahydrate and a methanol solution of dimethylimidazole to obtain a suspension, and centrifuging to obtain ZIF-8;

[0012] The mass ratio of zinc nitrate hexahydrate to dimethylimidazole is 1:2-1:3.

[0013] According to an embodiment of the present disclosure, in the first pyrolysis, the pyrolysis temperature is 800-1000° C., and the pyrolysis time is 0.5-2 h.

[0014] According to an embodiment of the present disclosure, the superoxide includes KO2, the crown ether includes 18-2 crown ether, the molar ratio of the superoxide to the crown ether is less than 0.9, and the mass ratio of the superoxide to the nitrogen-carbon substrate is 0.3-1.2.

[0015] According to an embodiment of the present disclosure, the iron salt includes any one of FeCl2 and FeSO4, and the mass ratio of the iron salt to the nitrogen-carbon substrate is greater than 0.1.

[0016] According to an embodiment of the present disclosure, in the second pyrolysis, the pyrolysis temperature is 800-1000° C., and the pyrolysis time is 0.5-2 h.

[0017] In another aspect of the present disclosure, an Fe-NC cathode oxygen reduction catalyst prepared by the aforementioned method is provided, comprising a nitrogen-carbon substrate and an active center. The nitrogen-carbon substrate has a regular dodecahedral framework structure with carbon-oxygen double bond defects on its surface; the active center is FeN4 supported within the framework structure.

[0018] According to an embodiment of the present disclosure, the mass fraction of the active center is 7.3 wt %-9.6 wt %.

[0019] In another aspect of the present disclosure, an application of the aforementioned Fe-NC cathode oxygen reduction catalyst in a fuel cell is also proposed.

[0020] According to the embodiment of the present disclosure, the peak power density of the fuel cell is 1491-1706 mW / cm 2 .

[0021] According to the embodiments of the present disclosure, superoxide ions released in a solution environment by the combination of superoxide and crown ether can achieve mild oxygen etching of the nitrogen-carbon substrate, and then a high-density Fe single-atom catalyst supported by oxygen-etched nitrogen-doped carbon is synthesized by mixing and grinding with iron salts and calcining in an inert atmosphere. This method promotes the FeO x The dispersion of the particles and the formation of single-atom Fe sites significantly enhance the catalyst's oxygen reduction activity and fuel cell performance. The Fe-NC cathode oxygen reduction catalyst prepared by this method exhibits excellent activity and battery performance. Furthermore, the method proposed in this disclosure is simple and easy to implement, making it suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a spherical aberration electron microscopy image of the oxygen-etched Fe-NC cathode oxygen reduction catalyst prepared in Example 1 of the present disclosure;

[0023] Figure 2 This is a Fourier transform X-ray extended edge absorption structure (FT-EXAFS) of the oxygen-etched Fe-NC cathode oxygen reduction catalyst prepared in Example 1 of the present disclosure;

[0024] Figure 3 Scanning electron microscope images of the oxygen-etched Fe-NC cathode oxygen reduction catalysts prepared in Examples 1, 4, 5, and 12 of the present disclosure, wherein a is a scanning electron microscope image of the oxygen-etched Fe-NC cathode oxygen reduction catalyst prepared in Example 1, b is a scanning electron microscope image of the oxygen-etched Fe-NC cathode oxygen reduction catalyst prepared in Example 4, c is a scanning electron microscope image of the oxygen-etched Fe-NC cathode oxygen reduction catalyst prepared in Example 5, and d is a scanning electron microscope image of the oxygen-etched Fe-NC cathode oxygen reduction catalyst prepared in Example 12;

[0025] Figure 4 The linear sweep voltammogram of the oxygen-etched Fe-NC cathode oxygen reduction catalyst prepared in Examples 1, 4, 5, and 12 of the present disclosure in a 0.1 M perchloric acid solution;

[0026] Figure 5 Polarization curves of the oxygen-etched Fe-NC cathode oxygen reduction catalyst prepared in Examples 1, 5, 8, 11, and 12 of the present disclosure in an H2-O2 proton exchange membrane fuel cell under a back pressure of 2 Bar. DETAILED DESCRIPTION

[0027] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0028] The endpoints of the ranges and any values ​​disclosed in this disclosure are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in this disclosure.

[0029] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise," "include," etc. used herein indicate the presence of the features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0030] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0031] It should be noted that, unless otherwise defined, technical or scientific terms used in this disclosure should have the ordinary meanings understood by persons of ordinary skill in the art to which this disclosure belongs. Where references to "first," "second," or the like are used throughout this disclosure, such references are intended solely to distinguish similar objects and should not be construed as indicating or implying their relative importance, order of precedence, or implicitly specifying the quantity of the technical features being referred to. References to "first," "second," or the like should be understood to be interchangeable where appropriate.

[0032] Similarly, in order to streamline the present disclosure and aid in understanding one or more of the various disclosed aspects, in the above description of exemplary embodiments of the present disclosure, the various features of the present disclosure are sometimes grouped together into a single embodiment, figure, or description thereof. Descriptions with reference to the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples" and the like mean that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in an appropriate manner.

[0033] In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the fact that ordinary technicians in this field can implement them. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by this disclosure.

[0034] In the process of realizing the present disclosure, it was found that nitrogen-doped carbon is the most commonly used support for Fe-based single-atom catalysts for acidic oxygen reduction, which often contains a small amount of oxygen. In the process of Fe single-atom formation, the metal precursor is often FeO x The high electronegative oxygen functional groups are beneficial to reduce FeO x The particle size of the catalyst is reduced and its dispersion on the substrate surface is promoted, thereby obtaining a high density of Fe single-atom sites during high-temperature pyrolysis. However, the presence of excessive oxygen functional groups may reduce the conductivity and oxygen reduction selectivity of the catalyst, which is not conducive to the activity expression and stability of the catalyst.

[0035] Therefore, the development of high-loaded iron single-atom fuel cell cathode catalysts based on oxygen-etched nitrogen-doped carbon supports must adopt appropriate strategies to control the type and content of functional groups in order to obtain excellent acidic oxygen reduction activity and stability.

[0036] The present disclosure provides a method for preparing an oxygen-etched Fe-NC cathode oxygen reduction catalyst, comprising the following steps S101 to S103:

[0037] Step S101: performing a first pyrolysis on ZIF-8 in a protective atmosphere to obtain a nitrogen-carbon substrate, wherein the nitrogen-carbon substrate has a regular dodecahedral framework structure.

[0038] Step S102: dispersing the nitrogen-carbon substrate, superoxide and crown ether in a solvent to obtain a suspension. In the suspension, superoxide releases superoxide ions, which form carbon-oxygen double bond defects with carbon atoms in the nitrogen-carbon substrate. The suspension is centrifuged to obtain a composite solid.

[0039] In some specific embodiments, the dispersion and stirring method is magnetic stirring, the dispersant is dimethyl sulfoxide, the rotation speed is 500-800 rpm, for example, 500 rpm, 550 rpm, 600 rpm, 650 rpm, 700 rpm, 750 rpm, 800 rpm, etc., and the time is 12 hours. The separation method is centrifugal separation, the rotation speed is 10,000 rpm, and the time is 3 minutes. The drying method is vacuum drying, the drying temperature is 40-80°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, etc., and the time is 12 hours.

[0040] Step S103: After grinding and mixing the composite solid and the iron salt, performing a second pyrolysis in a protective atmosphere, acid washing and drying, to obtain an oxygen-etched Fe-NC cathode oxygen reduction catalyst.

[0041] In some specific embodiments, the grinding method is planetary ball milling at a rotation speed of 300 rpm for 30 minutes. The pickling method is sulfuric acid pickling at a sulfuric acid concentration of 0.5 M for 6 hours. The separation method after pickling is suction filtration, and the filter cake is washed with 4L of ultrapure water. The drying method is vacuum drying at a drying temperature of 40-80°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, etc., for 12 hours.

[0042] According to the embodiments of the present disclosure, superoxide ions released in a solution environment by the combination of superoxide and crown ether can achieve mild oxygen etching of the nitrogen-carbon substrate, and then a high-density Fe single-atom catalyst supported by oxygen-etched nitrogen-doped carbon is synthesized by mixing and grinding with iron salts and calcining in an inert atmosphere. This method promotes the FeO x The dispersion of the particles and the formation of single-atom Fe sites significantly enhance the catalyst's oxygen reduction activity and fuel cell performance. The Fe-NC cathode oxygen reduction catalyst prepared by this method exhibits excellent activity and battery performance. Furthermore, the method proposed in this disclosure is simple and easy to implement, making it suitable for large-scale production.

[0043] According to an embodiment of the present disclosure, the preparation method of ZIF-8 includes:

[0044] Mixing a methanol solution of zinc nitrate hexahydrate and a methanol solution of dimethylimidazole to obtain a suspension, and centrifuging to obtain ZIF-8;

[0045] The mass ratio of zinc nitrate hexahydrate to dimethylimidazole is 1:2-1:3, for example, 3:6.5.

[0046] In some specific embodiments, Zn(NO₃)₂·6H₂O and 2-methylimidazole are separately dispersed in methanol at room temperature, preferably by magnetic stirring for 5 minutes. After 5 minutes of magnetic stirring, clear solutions A and B are obtained. Solutions A and B are then mixed, preferably by magnetic stirring at 500-800 rpm, and stirred at room temperature for 24 hours to obtain a suspension. The suspension is then centrifuged, preferably by centrifugation at 8000 rpm for 3 minutes, and washed three times with methanol, preferably by ultrasonic dispersion in methanol and further centrifugation at 10000 rpm for 3 minutes. Finally, ZIF-8 is dried in an oven at 40-80°C, preferably by vacuum drying for 12 hours.

[0047] According to an embodiment of the present disclosure, in the first pyrolysis, the pyrolysis method is tubular furnace pyrolysis, the atmosphere is argon, the pyrolysis temperature is 800-1000 ℃, for example, it can be 800 ℃, 850 ℃, 900 ℃, 950 ℃, 1000 ℃, etc., and the pyrolysis time is 0.5-2 h, for example, it can be 0.5 h, 1 h, 1.5 h, 2 h, etc.

[0048] According to an embodiment of the present disclosure, superoxide includes KO2, crown ether includes 18-2 crown ether, the molar ratio of superoxide to crown ether is less than 0.9, and the mass ratio of superoxide to nitrogen-carbon substrate is 0.3-1.2, for example, it can be 0.3, 0.6, 0.9, etc.

[0049] According to an embodiment of the present disclosure, the iron salt includes any one of FeCl2 and FeSO4, and the mass ratio of the iron salt to the nitrogen-carbon substrate is greater than 0.1.

[0050] According to an embodiment of the present disclosure, in the second pyrolysis, the pyrolysis temperature is 800-1000°C, for example, 800°C, 850°C, 900°C, 950°C, 1000°C, etc., and the pyrolysis time is 0.5-2 h, for example, 0.5 h, 1 h, 1.5 h, 2 h, etc.

[0051] In another aspect of the present disclosure, an Fe-NC cathode oxygen reduction catalyst prepared by the aforementioned method is provided, comprising a nitrogen-carbon substrate and an active center. The nitrogen-carbon substrate has a regular dodecahedral framework structure with carbon-oxygen double bond defects on its surface; the active center is FeN4 supported within the framework structure.

[0052] According to the embodiments of the present disclosure, compared with the Fe-based single-atom catalyst prepared by the conventional method, the present disclosure introduces oxygen functional groups to disperse Fe atoms, and the catalyst has a higher Fe metal loading and better oxygen reduction activity.

[0053] According to an embodiment of the present disclosure, the mass fraction of the active center is 7.3 wt %-9.6 wt %, for example, it can be 7.3 wt %, 7.4 wt %, 8.0 wt %, 8.8 wt %, 9.6 wt %, etc.

[0054] In another aspect of the present disclosure, an application of the aforementioned Fe-NC cathode oxygen reduction catalyst in a fuel cell is also proposed.

[0055] According to the embodiments of the present disclosure, the Fe sites of the oxygen-etched Fe-NC cathode oxygen reduction catalyst are well dispersed, and have excellent catalytic activity and fuel cell peak power density.

[0056] According to the embodiment of the present disclosure, the peak power density of the fuel cell is 1491-1706 mW / cm 2 .

[0057] It should be noted that the embodiments described are only part of the embodiments of the present disclosure, rather than all of the embodiments. Based on the embodiments of the present disclosure, other embodiments obtained by ordinary technicians in this field without making creative work are all within the scope of protection of the present disclosure.

[0058] Example 1

[0059] At room temperature, 3.5 g of Zn(NO3)2·6H2O was dispersed in 40 mL of methanol and 6 g of 2-methylimidazole was dispersed in 80 mL of methanol, respectively. After magnetic stirring for 5 min, clear solutions A and B were obtained. Solutions A and B were mixed and stirred at room temperature for 24 h to obtain a first suspension. The first suspension was centrifuged at 8000 rpm for 3 min, then washed three times with methanol at 10000 rpm for 3 min, and dried in a vacuum drying oven at 60 °C for 12 h to obtain ZIF-8, which was recorded as the first composite solid.

[0060] The first composite solid was pyrolyzed at 950 °C under argon for 1 h to obtain a nitrogen-carbon substrate, which was recorded as the second composite solid.

[0061] 100 mg of the second composite solid, 59.3 mg of KO2, and 264.3 mg of 18-2 crown ether were dispersed in 100 mL of dimethyl sulfoxide solution and magnetically stirred for 12 h to obtain a second suspension. The second suspension was centrifuged and dried in a vacuum drying oven at 60 °C for 12 h to obtain a third composite solid.

[0062] 100 mg of the third composite solid was mixed with 20 mg of FeCl2·4H2O and subjected to planetary ball milling at 300 rpm for 30 minutes. The mixture was then pyrolyzed at 900°C under argon for 1 hour to produce a fourth composite solid. The fourth composite solid was acid-washed with 0.5 M sulfuric acid for 6 hours, then filtered and the filter cake washed with 4 L of ultrapure water. The filter cake was dried in a vacuum oven at 60°C for 12 hours to obtain an oxygen-etched Fe-NC cathode oxygen reduction catalyst (denoted as O-FeNC). The oxygen-etched Fe-NC catalyst prepared in Example 1 had an Fe loading of approximately 9.6 wt%.

[0063] The oxygen-etched Fe-NC cathode oxygen reduction catalyst of Example 1 was characterized by scanning electron microscopy.

[0064] The oxygen-etched Fe-NC cathode oxygen reduction catalyst of Example 1 was characterized by spherical aberration electron microscopy.

[0065] Figure 1 This is a spherical aberration electron microscopy image of the oxygen-etched Fe-NC cathode oxygen reduction catalyst prepared in Example 1 of the present disclosure.

[0066] like Figure 1 As shown, at the scale of 2 nm, there are highly dense and dispersed Fe single atoms in the catalyst, and there is no agglomeration phenomenon, which further verifies that the preparation method of oxygen-etched Fe-NC cathode oxygen reduction catalyst proposed in this disclosure can ensure that the active centers are uniformly dispersed and not agglomerated under the condition of high active center density (Fe loading 9.6 wt%).

[0067] The oxygen-etched Fe-NC cathode oxygen reduction catalyst of Example 1 was subjected to X-ray absorption spectroscopy analysis.

[0068] Figure 2 This is the Fourier transform X-ray extended edge absorption structure (FT-EXAFS) of the oxygen-etched Fe-NC cathode oxygen reduction catalyst prepared in Example 1 of the present disclosure.

[0069] like Figure 2 As shown, the oxygen-etched Fe-NC cathode oxygen reduction catalyst (O-FeNC catalyst) prepared in Example 1 contains only Fe-N / O bonds with a bond length of approximately 1.4 Å in the first shell, while Fe-Fe bonds with a bond length of 2.1-2.3 Å in the second shell are absent. This further verifies that the preparation method of the oxygen-etched Fe-NC cathode oxygen reduction catalyst proposed in this disclosure can ensure uniform dispersion of active centers without agglomeration under conditions of high active center density.

[0070] Example 2

[0071] At room temperature, 3.5 g of Zn(NO3)2·6H2O was dispersed in 40 mL of methanol and 6 g of 2-methylimidazole was dispersed in 80 mL of methanol, respectively. After magnetic stirring for 5 min, clear solutions A and B were obtained. Solutions A and B were mixed and stirred at room temperature for 24 h to obtain a first suspension. The first suspension was centrifuged at 8000 rpm for 3 min, then washed three times with methanol at 10000 rpm for 3 min, and dried in a vacuum drying oven at 60 °C for 12 h to obtain ZIF-8, which was recorded as the first composite solid.

[0072] The first composite solid was pyrolyzed at 850 °C under argon for 1 h to obtain a nitrogen-carbon substrate, which was recorded as the second composite solid.

[0073] 100 mg of the second composite solid, 59.3 mg of KO2, and 264.3 mg of 18-2 crown ether were dispersed in 100 mL of dimethyl sulfoxide solution and magnetically stirred for 12 h to obtain a second suspension. The second suspension was centrifuged and dried in a vacuum drying oven at 60 °C for 12 h to obtain a third composite solid.

[0074] 100 mg of the third composite solid was mixed with 20 mg of FeCl2·4H2O and subjected to planetary ball milling at 300 rpm for 30 minutes. The mixture was then pyrolyzed at 900°C under argon for 1 hour to produce a fourth composite solid. The fourth composite solid was acid-washed with 0.5 M sulfuric acid for 6 hours, then filtered and the filter cake washed with 4 L of ultrapure water. The filter cake was dried in a vacuum oven at 60°C for 12 hours to obtain an oxygen-etched Fe-NC cathode oxygen reduction catalyst. The oxygen-etched Fe-NC catalyst prepared in Example 2 had an Fe loading of approximately 8.0 wt%.

[0075] The oxygen-etched Fe-NC cathode oxygen reduction catalyst of Example 2 was subjected to spherical aberration electron microscopy, X-ray absorption spectroscopy, linear sweep voltammetry, and fuel cell polarization analysis, and the results were similar to those of Example 1.

[0076] Example 3

[0077] At room temperature, 3.5 g of Zn(NO3)2·6H2O was dispersed in 40 mL of methanol and 6 g of 2-methylimidazole was dispersed in 80 mL of methanol, respectively. After magnetic stirring for 5 min, clear solutions A and B were obtained. Solutions A and B were mixed and stirred at room temperature for 24 h to obtain a first suspension. The first suspension was centrifuged at 8000 rpm for 3 min, then washed three times with methanol at 10000 rpm for 3 min, and dried in a vacuum drying oven at 60 °C for 12 h to obtain ZIF-8, which was recorded as the first composite solid.

[0078] The first composite solid was pyrolyzed at 1000 °C under argon for 1 h to obtain a nitrogen-carbon substrate, which was recorded as the second composite solid.

[0079] 100 mg of the second composite solid, 59.3 mg of KO2, and 264.3 mg of 18-2 crown ether were dispersed in 100 mL of dimethyl sulfoxide solution and magnetically stirred for 12 h to obtain a second suspension. The second suspension was centrifuged and dried in a vacuum drying oven at 60 °C for 12 h to obtain a third composite solid.

[0080] 100 mg of the third composite solid was mixed with 20 mg of FeCl2·4H2O and subjected to planetary ball milling at 300 rpm for 30 minutes. The mixture was then pyrolyzed at 900°C under argon for 1 hour to produce a fourth composite solid. The fourth composite solid was acid-washed with 0.5 M sulfuric acid for 6 hours, then filtered and the filter cake washed with 4 L of ultrapure water. The filter cake was dried in a vacuum oven at 60°C for 12 hours to obtain an oxygen-etched Fe-NC cathode oxygen reduction catalyst. The oxygen-etched Fe-NC catalyst prepared in Example 3 had an Fe loading of approximately 8.2 wt%.

[0081] The oxygen-etched Fe-NC cathode oxygen reduction catalyst of Example 3 was subjected to spherical aberration electron microscopy, X-ray absorption spectroscopy, linear sweep voltammetry, and fuel cell polarization analysis, and the results were similar to those of Example 1.

[0082] Example 4

[0083] At room temperature, 3.5 g of Zn(NO3)2·6H2O was dispersed in 40 mL of methanol and 6 g of 2-methylimidazole was dispersed in 80 mL of methanol, respectively. After magnetic stirring for 5 min, clear solutions A and B were obtained. Solutions A and B were mixed and stirred at room temperature for 24 h to obtain a first suspension. The first suspension was centrifuged at 8000 rpm for 3 min, then washed three times with methanol at 10000 rpm for 3 min, and dried in a vacuum drying oven at 60 °C for 12 h to obtain ZIF-8, which was recorded as the first composite solid.

[0084] The first composite solid was pyrolyzed at 950 °C under argon for 1 h to obtain a nitrogen-carbon substrate, which was recorded as the second composite solid.

[0085] 100 mg of the second composite solid, 29.7 mg of KO2, and 132.2 mg of 18-2 crown ether were dispersed in 100 mL of dimethyl sulfoxide solution and magnetically stirred for 12 h to obtain a second suspension. The second suspension was centrifuged and dried in a vacuum drying oven at 60 °C for 12 h to obtain a third composite solid.

[0086] 100 mg of the third composite solid was mixed with 20 mg of FeCl2·4H2O and subjected to planetary ball milling at 300 rpm for 30 minutes. The mixture was then pyrolyzed at 900°C under argon for 1 hour to produce a fourth composite solid. The fourth composite solid was then acid-washed with 0.5 M sulfuric acid for 6 hours. The filter cake was then filtered and washed with 4 L of ultrapure water. The filter cake was dried in a vacuum oven at 60°C for 12 hours to obtain an oxygen-etched Fe-NC cathode oxygen reduction catalyst. The oxygen-etched Fe-NC catalyst prepared in Example 4 had an Fe loading of approximately 8.6 wt%.

[0087] The oxygen-etched Fe-NC cathode oxygen reduction catalyst of Example 4 was subjected to spherical aberration electron microscopy, X-ray absorption spectroscopy, linear sweep voltammetry, and fuel cell polarization analysis, and the results were similar to those of Example 1.

[0088] Example 5

[0089] At room temperature, 3.5 g of Zn(NO3)2·6H2O was dispersed in 40 mL of methanol and 6 g of 2-methylimidazole was dispersed in 80 mL of methanol, respectively. After magnetic stirring for 5 min, clear solutions A and B were obtained. Solutions A and B were mixed and stirred at room temperature for 24 h to obtain a first suspension. The first suspension was centrifuged at 8000 rpm for 3 min, then washed three times with methanol at 10000 rpm for 3 min, and dried in a vacuum drying oven at 60 °C for 12 h to obtain ZIF-8, which was recorded as the first composite solid.

[0090] The first composite solid was pyrolyzed at 950 °C under argon for 1 h to obtain a nitrogen-carbon substrate, which was recorded as the second composite solid.

[0091] 100 mg of the second composite solid, 118.6 mg of KO2, and 528.6 mg of 18-2 crown ether were dispersed in 100 mL of dimethyl sulfoxide solution and magnetically stirred for 12 h to obtain a second suspension. The second suspension was centrifuged and dried in a vacuum drying oven at 60 °C for 12 h to obtain a third composite solid.

[0092] 100 mg of the third composite solid was mixed with 20 mg of FeCl2·4H2O and subjected to planetary ball milling at 300 rpm for 30 minutes. The mixture was then pyrolyzed at 900°C under argon for 1 hour to produce a fourth composite solid. The fourth composite solid was acid-washed with 0.5 M sulfuric acid for 6 hours, then filtered and the filter cake washed with 4 L of ultrapure water. The filter cake was dried in a vacuum oven at 60°C for 12 hours to obtain an oxygen-etched Fe-NC cathode oxygen reduction catalyst. The oxygen-etched Fe-NC catalyst prepared in Example 5 had an Fe loading of approximately 9.3 wt%.

[0093] The oxygen-etched Fe-NC cathode oxygen reduction catalyst of Example 5 was subjected to spherical aberration electron microscopy, X-ray absorption spectroscopy, linear sweep voltammetry, and fuel cell polarization analysis, and the results were similar to those of Example 1.

[0094] Example 6

[0095] At room temperature, 3.5 g of Zn(NO3)2·6H2O was dispersed in 40 mL of methanol and 6 g of 2-methylimidazole was dispersed in 80 mL of methanol, respectively. After magnetic stirring for 5 min, clear solutions A and B were obtained. Solutions A and B were mixed and stirred at room temperature for 24 h to obtain a first suspension. The first suspension was centrifuged at 8000 rpm for 3 min, then washed three times with methanol at 10000 rpm for 3 min, and dried in a vacuum drying oven at 60 °C for 12 h to obtain ZIF-8, which was recorded as the first composite solid.

[0096] The first composite solid was pyrolyzed at 950 °C under argon for 1 h to obtain a nitrogen-carbon substrate, which was recorded as the second composite solid.

[0097] 100 mg of the second composite solid, 59.3 mg of KO2, and 264.3 mg of 18-2 crown ether were dispersed in 100 mL of dimethyl sulfoxide solution and magnetically stirred for 12 h to obtain a second suspension. The second suspension was centrifuged and dried in a vacuum drying oven at 60 °C for 12 h to obtain a third composite solid.

[0098] 100 mg of the third composite solid was mixed with 20 mg of FeCl2·4H2O and subjected to planetary ball milling at 300 rpm for 30 minutes. The mixture was then pyrolyzed at 800°C under argon for 1 hour to produce a fourth composite solid. The fourth composite solid was acid-washed with 0.5 M sulfuric acid for 6 hours, then filtered and the filter cake washed with 4 L of ultrapure water. The filter cake was dried in a vacuum oven at 60°C for 12 hours to obtain an oxygen-etched Fe-NC cathode oxygen reduction catalyst. The oxygen-etched Fe-NC catalyst prepared in Example 6 had an Fe loading of approximately 9.1 wt%.

[0099] The oxygen-etched Fe-NC cathode oxygen reduction catalyst of Example 6 was subjected to spherical aberration electron microscopy, X-ray absorption spectroscopy, linear sweep voltammetry, and fuel cell polarization analysis, and the results were similar to those of Example 1.

[0100] Example 7

[0101] At room temperature, 3.5 g of Zn(NO3)2·6H2O was dispersed in 40 mL of methanol and 6 g of 2-methylimidazole was dispersed in 80 mL of methanol, respectively. After magnetic stirring for 5 min, clear solutions A and B were obtained. Solutions A and B were mixed and stirred at room temperature for 24 h to obtain a first suspension. The first suspension was centrifuged at 8000 rpm for 3 min, then washed three times with methanol at 10000 rpm for 3 min, and dried in a vacuum drying oven at 60 °C for 12 h to obtain ZIF-8, which was recorded as the first composite solid.

[0102] The first composite solid was pyrolyzed at 950 °C under argon for 1 h to obtain a nitrogen-carbon substrate, which was recorded as the second composite solid.

[0103] 100 mg of the second composite solid, 59.3 mg of KO2, and 264.3 mg of 18-2 crown ether were dispersed in 100 mL of dimethyl sulfoxide solution and magnetically stirred for 12 h to obtain a second suspension. The second suspension was centrifuged and dried in a vacuum drying oven at 60 °C for 12 h to obtain a third composite solid.

[0104] 100 mg of the third composite solid was mixed with 20 mg of FeCl2·4H2O and subjected to planetary ball milling at 300 rpm for 30 minutes. The mixture was then pyrolyzed at 1000°C under argon for 1 hour to produce a fourth composite solid. The fourth composite solid was acid-washed with 0.5 M sulfuric acid for 6 hours, then filtered and the filter cake washed with 4 L of ultrapure water. The filter cake was dried in a vacuum oven at 60°C for 12 hours to obtain an oxygen-etched Fe-NC cathode oxygen reduction catalyst. The oxygen-etched Fe-NC catalyst prepared in Example 7 had an Fe loading of approximately 8.0 wt%.

[0105] The oxygen-etched Fe-NC cathode oxygen reduction catalyst of Example 7 was subjected to spherical aberration electron microscopy, X-ray absorption spectroscopy, linear sweep voltammetry, and fuel cell polarization analysis, and the results were similar to those of Example 1.

[0106] Example 8

[0107] At room temperature, 3.5 g of Zn(NO3)2·6H2O was dispersed in 40 mL of methanol and 6 g of 2-methylimidazole was dispersed in 80 mL of methanol, respectively. After magnetic stirring for 5 min, clear solutions A and B were obtained. Solutions A and B were mixed and stirred at room temperature for 24 h to obtain a first suspension. The first suspension was centrifuged at 8000 rpm for 3 min, then washed three times with methanol at 10000 rpm for 3 min, and dried in a vacuum drying oven at 60 °C for 12 h to obtain ZIF-8, which was recorded as the first composite solid.

[0108] The first composite solid was pyrolyzed at 950 °C under argon for 1 h to obtain a nitrogen-carbon substrate, which was recorded as the second composite solid.

[0109] 100 mg of the second composite solid, 59.3 mg of KO2, and 264.3 mg of 18-2 crown ether were dispersed in 100 mL of dimethyl sulfoxide solution and magnetically stirred for 12 h to obtain a second suspension. The second suspension was centrifuged and dried in a vacuum drying oven at 60 °C for 12 h to obtain a third composite solid.

[0110] 100 mg of the third composite solid was mixed with 20 mg of FeCl2·4H2O and subjected to planetary ball milling at 300 rpm for 30 minutes. The mixture was then pyrolyzed at 900°C under argon for 2 hours to produce a fourth composite solid. The fourth composite solid was acid-washed with 0.5 M sulfuric acid for 6 hours, then filtered and the filter cake washed with 4 L of ultrapure water. The filter cake was dried in a vacuum oven at 60°C for 12 hours to obtain an oxygen-etched Fe-NC cathode oxygen reduction catalyst. The oxygen-etched Fe-NC catalyst prepared in Example 8 had an Fe loading of approximately 7.9 wt%.

[0111] The oxygen-etched Fe-NC cathode oxygen reduction catalyst of Example 8 was subjected to spherical aberration electron microscopy, X-ray absorption spectroscopy, linear sweep voltammetry, and fuel cell polarization analysis, and the results were similar to those of Example 1.

[0112] Example 9

[0113] At room temperature, 3.5 g of Zn(NO3)2·6H2O was dispersed in 40 mL of methanol and 6 g of 2-methylimidazole was dispersed in 80 mL of methanol, respectively. After magnetic stirring for 5 min, clear solutions A and B were obtained. Solutions A and B were mixed and stirred at room temperature for 24 h to obtain a first suspension. The first suspension was centrifuged at 8000 rpm for 3 min, then washed three times with methanol at 10000 rpm for 3 min, and dried in a vacuum drying oven at 60 °C for 12 h to obtain ZIF-8, which was recorded as the first composite solid.

[0114] The first composite solid was pyrolyzed at 950 °C under argon for 1 h to obtain a nitrogen-carbon substrate, which was recorded as the second composite solid.

[0115] 100 mg of the second composite solid, 59.3 mg of KO2, and 264.3 mg of 18-2 crown ether were dispersed in 100 mL of dimethyl sulfoxide solution and magnetically stirred for 12 h to obtain a second suspension. The second suspension was centrifuged and dried in a vacuum drying oven at 60 °C for 12 h to obtain a third composite solid.

[0116] 100 mg of the third composite solid was mixed with 38.4 mg of FeSO₄·7H₂O and subjected to planetary ball milling at 300 rpm for 30 minutes. The mixture was then pyrolyzed at 900°C under argon for 1 hour to produce a fourth composite solid. The fourth composite solid was acid-washed with 0.5 M sulfuric acid for 6 hours, then filtered and the filter cake washed with 4 L of ultrapure water. The filter cake was dried in a vacuum oven at 60°C for 12 hours to obtain an oxygen-etched Fe-NC cathode oxygen reduction catalyst. The oxygen-etched Fe-NC catalyst prepared in Example 9 had an Fe loading of approximately 7.3 wt%.

[0117] The oxygen-etched Fe-NC cathode oxygen reduction catalyst of Example 9 was subjected to spherical aberration electron microscopy, X-ray absorption spectroscopy, linear sweep voltammetry, and fuel cell polarization analysis, and the results were similar to those of Example 1.

[0118] Example 10

[0119] At room temperature, 3.5 g of Zn(NO3)2·6H2O was dispersed in 40 mL of methanol and 6 g of 2-methylimidazole was dispersed in 80 mL of methanol, respectively. After magnetic stirring for 5 min, clear solutions A and B were obtained. Solutions A and B were mixed and stirred at room temperature for 24 h to obtain a first suspension. The first suspension was centrifuged at 8000 rpm for 3 min, then washed three times with methanol at 10000 rpm for 3 min, and dried in a vacuum drying oven at 60 °C for 12 h to obtain ZIF-8, which was recorded as the first composite solid.

[0120] The first composite solid was pyrolyzed at 950 °C under argon for 1 h to obtain a nitrogen-carbon substrate, which was recorded as the second composite solid.

[0121] 100 mg of the second composite solid, 59.3 mg of KO2, and 264.3 mg of 18-2 crown ether were dispersed in 100 mL of dimethyl sulfoxide solution and magnetically stirred for 12 h to obtain a second suspension. The second suspension was centrifuged and dried in a vacuum drying oven at 60 °C for 12 h to obtain a third composite solid.

[0122] 100 mg of the third composite solid was mixed with 5 mg of FeCl2·4H2O and subjected to planetary ball milling at 300 rpm for 30 minutes. The mixture was then pyrolyzed at 900°C under argon for 1 hour to produce a fourth composite solid. The fourth composite solid was acid-washed with 0.5 M sulfuric acid for 6 hours, then filtered and the filter cake washed with 4 L of ultrapure water. The filter cake was dried in a vacuum oven at 60°C for 12 hours to obtain an oxygen-etched Fe-NC cathode oxygen reduction catalyst. The oxygen-etched Fe-NC catalyst prepared in Example 10 had an Fe loading of approximately 7.4 wt%.

[0123] The oxygen-etched Fe-NC cathode oxygen reduction catalyst of Example 10 was subjected to spherical aberration electron microscopy, X-ray absorption spectroscopy, linear sweep voltammetry, and fuel cell polarization analysis, and the results were similar to those of Example 1.

[0124] Example 11

[0125] At room temperature, 3.5 g of Zn(NO3)2·6H2O was dispersed in 40 mL of methanol and 6 g of 2-methylimidazole was dispersed in 80 mL of methanol, respectively. After magnetic stirring for 5 min, clear solutions A and B were obtained. Solutions A and B were mixed and stirred at room temperature for 24 h to obtain a first suspension. The first suspension was centrifuged at 8000 rpm for 3 min, then washed three times with methanol at 10000 rpm for 3 min, and dried in a vacuum drying oven at 60 °C for 12 h to obtain ZIF-8, which was recorded as the first composite solid.

[0126] The first composite solid was pyrolyzed at 950 °C under argon for 1 h to obtain a nitrogen-carbon substrate, which was recorded as the second composite solid.

[0127] 100 mg of the second composite solid, 59.3 mg of KO2, and 264.3 mg of 18-2 crown ether were dispersed in 100 mL of dimethyl sulfoxide solution and magnetically stirred for 12 h to obtain a second suspension. The second suspension was centrifuged and dried in a vacuum drying oven at 60 °C for 12 h to obtain a third composite solid.

[0128] 100 mg of the third composite solid was mixed with 10 mg of FeCl2·4H2O and subjected to planetary ball milling at 300 rpm for 30 minutes. The mixture was then pyrolyzed at 900°C under argon for 1 hour to produce a fourth composite solid. The fourth composite solid was acid-washed with 0.5 M sulfuric acid for 6 hours, then filtered and the filter cake washed with 4 L of ultrapure water. The filter cake was dried in a vacuum oven at 60°C for 12 hours to obtain an oxygen-etched Fe-NC cathode oxygen reduction catalyst. The oxygen-etched Fe-NC catalyst prepared in Example 11 had an Fe loading of approximately 8.9 wt%.

[0129] The oxygen-etched Fe-NC cathode oxygen reduction catalyst of Example 11 was subjected to spherical aberration electron microscopy, X-ray absorption spectroscopy, linear sweep voltammetry, and fuel cell polarization analysis, and the results were similar to those of Example 1.

[0130] Example 12

[0131] At room temperature, 3.5 g of Zn(NO3)2·6H2O was dispersed in 40 mL of methanol and 6 g of 2-methylimidazole was dispersed in 80 mL of methanol, respectively. After magnetic stirring for 5 min, clear solutions A and B were obtained. Solutions A and B were mixed and stirred at room temperature for 24 h to obtain a first suspension. The first suspension was centrifuged at 8000 rpm for 3 min, then washed three times with methanol at 10000 rpm for 3 min, and dried in a vacuum drying oven at 60 °C for 12 h to obtain ZIF-8, which was recorded as the first composite solid.

[0132] The first composite solid was pyrolyzed at 950 °C under argon for 1 h to obtain a nitrogen-carbon substrate, which was recorded as the second composite solid.

[0133] 100 mg of the second composite solid, 59.3 mg of KO2, and 264.3 mg of 18-2 crown ether were dispersed in 100 mL of dimethyl sulfoxide solution and magnetically stirred for 12 h to obtain a second suspension. The second suspension was centrifuged and dried in a vacuum drying oven at 60 °C for 12 h to obtain a third composite solid.

[0134] 100 mg of the third composite solid was mixed with 40 mg of FeCl2·4H2O and subjected to planetary ball milling at 300 rpm for 30 minutes. The resulting composite solid was then pyrolyzed at 900°C under argon for 1 hour to produce the fourth composite solid. The fourth composite solid was then acid-washed with 0.5 M sulfuric acid for 6 hours. The filter cake was then filtered and washed with 4 L of ultrapure water. The filter cake was then dried in a vacuum oven at 60°C for 12 hours to obtain an oxygen-etched Fe-NC cathode oxygen reduction catalyst. The oxygen-etched Fe-NC catalyst prepared in Example 12 had an Fe loading of approximately 9.2 wt%.

[0135] The oxygen-etched Fe-NC cathode oxygen reduction catalyst of Example 12 was subjected to spherical aberration electron microscopy, X-ray absorption spectroscopy, linear sweep voltammetry, and fuel cell polarization analysis, and the results were similar to those of Example 1.

[0136] Figure 3 These are scanning electron microscope images of the oxygen-etched Fe-NC cathode oxygen reduction catalysts prepared in Examples 1, 4, 5, and 12 of the present disclosure, wherein a is a scanning electron microscope image of the oxygen-etched Fe-NC cathode oxygen reduction catalyst prepared in Example 1, b is a scanning electron microscope image of the oxygen-etched Fe-NC cathode oxygen reduction catalyst prepared in Example 4, c is a scanning electron microscope image of the oxygen-etched Fe-NC cathode oxygen reduction catalyst prepared in Example 5, and d is a scanning electron microscope image of the oxygen-etched Fe-NC cathode oxygen reduction catalyst prepared in Example 12.

[0137] like Figure 3As shown, at a scale of 100 nm, the catalyst particles are a framework structure of regular dodecahedrons with a diameter of about 200 nm. The material prepared in Example 1 does not have obvious particles at this scale.

[0138] The oxygen-etched Fe-NC cathode oxygen reduction catalysts prepared in Examples 1, 4, 5, and 12 were subjected to linear sweep voltammetry tests in 0.1 M perchloric acid solution.

[0139] Figure 4 Linear sweep voltammograms of the oxygen-etched Fe-NC cathode oxygen reduction catalysts prepared in Examples 1, 4, 5, and 12 of the present disclosure in a 0.1 M perchloric acid solution.

[0140] like Figure 4 As shown, the oxygen-etched Fe-NC cathode oxygen reduction catalyst prepared in Example 1 exhibited excellent acidic oxygen reduction activity, with a half-wave potential of 0.881 V, 0.875 V for Example 4, 0.874 V for Example 5, and 0.861 V for Example 12. These performances were superior to those of a commercial platinum-carbon catalyst (Pt / C, 0.86 V) and a conventional Fe-NC cathode oxygen reduction catalyst (FeNC, 0.825 V). This demonstrates that the oxygen-etched Fe-NC cathode oxygen reduction catalyst prepared in Example 1 exhibits high electrode activity in electrochemical reactions and can more effectively promote the electrochemical reaction. The optimal catalyst preparation parameters should be as shown in Example 1.

[0141] The oxygen-etched Fe-NC cathode oxygen reduction catalysts prepared in Examples 1, 5, 8, 11, and 12 were subjected to H2-O2 proton exchange membrane fuel cell polarization tests at a back pressure of 2 Bar.

[0142] Figure 5 Polarization curves of the oxygen-etched Fe-NC cathode oxygen reduction catalyst prepared in Examples 1, 5, 8, 11, and 12 of the present disclosure in an H2-O2 proton exchange membrane fuel cell under a back pressure of 2 Bar.

[0143] like Figure 5 As shown in FIG, the peak power density of the oxygen-etched Fe-NC cathode oxygen reduction catalyst prepared in Example 1 of the present disclosure is 1706 mW / cm 2 The peak power density of Example 5 is 1491 mW / cm 2 The peak power density of Example 8 is 1553 mW / cm 2 The peak power density of Example 11 is 1631 mW / cm 2 The peak power density of Example 12 is 1627 mW / cm 2The peak power density of the conventional Fe-NC cathode oxygen reduction catalyst is 783 mW / cm 2 It can be seen that the oxygen-etched Fe-NC cathode oxygen reduction catalyst prepared in Example 1 exhibits excellent peak power density. The optimal catalyst preparation parameters should be as shown in Example 1.

[0144] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present disclosure in detail. It should be understood that the above are only specific embodiments of the present disclosure and are not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure should be included in the scope of protection of the present disclosure.

Claims

1. A method for preparing an oxygen-etched Fe-NC cathode oxygen reduction catalyst, comprising: In a protective atmosphere, ZIF-8 is subjected to a first pyrolysis to obtain a nitrogen-carbon substrate, wherein the nitrogen-carbon substrate has a regular dodecahedral framework structure; Dispersing the nitrogen-carbon substrate, superoxide, and crown ether in a solvent to obtain a suspension, wherein the superoxide releases superoxide ions in the suspension, and the superoxide ions form carbon-oxygen double bond defects with carbon atoms in the nitrogen-carbon substrate, and centrifuging the suspension to obtain a composite solid; The composite solid is ground and mixed with iron salt, and then subjected to a second pyrolysis in a protective atmosphere. After acid washing and drying, an oxygen-etched Fe-NC cathode oxygen reduction catalyst is obtained.

2. The preparation method according to claim 1, wherein The preparation method of the ZIF-8 comprises: Mixing a methanol solution of zinc nitrate hexahydrate and a methanol solution of dimethylimidazole to obtain a suspension, and centrifuging to obtain ZIF-8; Wherein, the mass ratio of the zinc nitrate hexahydrate to dimethylimidazole is 1:2-1:

3.

3. The preparation method according to claim 1, wherein In the first pyrolysis, the pyrolysis temperature is 800-1000° C., and the pyrolysis time is 0.5-2 h.

4. The preparation method according to claim 1, wherein The superoxide includes KO2, the crown ether includes 18-2 crown ether, the molar ratio of the superoxide to the crown ether is less than 0.9, and the mass ratio of the superoxide to the nitrogen-carbon substrate is 0.3-1.

2.

5. The preparation method according to claim 1, wherein The iron salt includes any one of FeCl2 and FeSO4, and the mass ratio of the iron salt to the nitrogen-carbon substrate is greater than 0.

1.

6. The preparation method according to claim 1, wherein In the second pyrolysis, the pyrolysis temperature is 800-1000° C., and the pyrolysis time is 0.5-2 h.

7. An Fe-NC cathode oxygen reduction catalyst obtained by the preparation method according to any one of claims 1 to 6, comprising: A nitrogen-carbon substrate having a regular dodecahedral framework structure, wherein a surface of the nitrogen-carbon substrate includes carbon-oxygen double bond defects; Active center, the active center is FeN4 loaded in the framework structure.

8. The Fe-NC cathode oxygen reduction catalyst according to claim 7, wherein The mass fraction of the active center is 7.3 wt %-9.6 wt %.

9. Use of the Fe-NC cathode oxygen reduction catalyst according to any one of claims 7 or 8 in a fuel cell.

10. The use according to claim 9, wherein: The peak power density of the fuel cell is 1491-1706 mW / cm 2 .

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